The formation and maturation of calcium phosphate prepared from physiological-like solutions is being studied with a number of physical-chemical and ultrastructural techniques including standard analytical chemistry procedures, electron microscopy and x-ray diffraction. Topics of present interest include (1) phase changes in calcium phosphate preparations resulting from aging in aqueous media; (2) effect ionic fluoride on the formation and growth of crystalline apatite. BIBLIOGRAPHIC REFERENCES: Eanes, E.D.: The interaction of supersaturated calcium phosphate solutions with apatitic substrates. Calcif. Tiss. Res. 20: 75-89, 1976. Eanes, E.D., Martin, G.N., and Lundy, D.R.: The distribution of water in calcified turkey leg tendon. Calcif. Tiss. Res. 20: 313-316, 1976.